A quantitative assessment of methane cycling in <scp>H</scp>ikurangi <scp>M</scp>argin sediments (<scp>N</scp>ew <scp>Z</scp>ealand) using geophysical imaging and biogeochemical modeling

Luo, Min; Dale, Andrew W.; Haffert, Laura; Haeckel, Matthias; Koch, Stephanie; Crutchley, Gareth; Stigter, Henko de; Chen, Duofu; Greinert, Jens

doi:10.1002/2016gc006643

Cited by 22 publications

(18 citation statements)

References 90 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The SO 4 2concentrations in 2015XS-50 and 2015XS-R2 display near-seawater values in the upper 3-5 meters and then decline sharply towards the SMTZ. The seawater intrusion feature is also reflected by calcium concentration profiles, which is attributed to the irrigation of porewater caused by gas bubbling as demonstrated by previous studies [26,52,53]. At core 2015XS-44, the sulfate concentration profile does not show the feature of bubble irrigation but the calcium concentration profile still exhibits a kink at~5 mbsf.…”

Section: Porewater Geochemistrysupporting

confidence: 52%

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

Zhang

Luo

et al. 2019

Geofluids

Self Cite

View full text Add to dashboard Cite

Gas hydrates, acting as a dynamic methane reservoir, store methane in the form of a solid phase under high-pressure and low-temperature conditions and release methane through the sediment column into seawater when they are decomposed. The seepage of methane-rich fluid (i.e., cold hydrocarbon seeps) fuels the chemosynthetic biota-inhabited surface sediments and represents the major pathway to transfer carbon from sediments to the water column. Generally, the major biogeochemical reactions related to carbon cycling in the anoxic marine sediments include organic matter degradation via sulfate reduction (OSR), anaerobic oxidation of methane (AOM), methanogenesis (ME), and carbonate precipitation (CP). In order to better understand the carbon turnover in the cold seeps and gas hydrate-bearing areas of the northern South China Sea (SCS), we collected geochemical data of 358 cores from published literatures and retrieved 37 cores and corresponding pore water samples from three areas of interest (i.e., Xisha, Dongsha, and Shenhu areas). Reaction-transport simulations indicate that the rates of organic matter degradation and carbonate precipitation are comparable in the three areas, while the rates of AOM vary over several orders of magnitude (AOM: 8.3-37.5 mmol·m-2·yr-1 in Dongsha, AOM: 12.4-170.6 mmol·m-2·yr-1 in Xisha, and AOM: 9.4-30.5 mmol·m-2·yr-1 in Shenhu). Both the arithmetical mean and interpolation mean of the biogeochemical processes were calculated in each area. Averaging these two mean values suggested that the rates of organic matter degradation in Dongsha (25.7 mmol·m-2·yr-1) and Xisha (25.1 mmol·m-2·yr-1) are higher than that in Shenhu (12 mmol·m-2·yr-1) and the AOM rate in Xisha (135.2 mmol·m-2·yr-1) is greater than those in Dongsha (27.8 mmol·m-2·yr-1) and Shenhu (17.5 mmol·m-2·yr-1). In addition, the rate of carbonate precipitation (32.3 mmol·m-2·yr-1) in Xisha is far higher than those of the other two regions (5.3 mmol·m-2·yr-1 in Dongsha, 5.8 mmol·m-2·yr-1 in Shenhu) due to intense AOM sustained by gas dissolution. In comparison with other cold seeps around the world, the biogeochemical rates in the northern SCS are generally lower than those in active continental margins and special environments (e.g., the Black sea) but are comparable with those in passive continental margins. Collectively, ~2.8 Gmol organic matter was buried and at least ~0.82 Gmol dissolved organic and inorganic carbon was diffused out of sediments annually. This may, to some extent, have an impact on the long-term deep ocean carbon cycle in the northern SCS.

show abstract

Section: Porewater Geochemistrysupporting

confidence: 52%

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

Zhang

Luo

et al. 2019

Geofluids

Self Cite

View full text Add to dashboard Cite

show abstract

“…Separated from the continental slope by erosive canyons (Lewis, et al 1998) and delimited in the south by the Hikurangi Trough (Barnes et al, 2010), the SE flank of Opouawe Bank is characterized by gullies and the NW flank by translational landslide scars (Law et al, 2010). The most recent sediments on the ridge top are hemipelagic mud and turbidity current overspill deposits (Lewis et al, 1998;Luo et al, 2016). The tectonic structure of the Wairarapa area is dominated by three major sub-parallel fault systems; these are, from north to south, the strike-slip Boo Boo Fault, and the Opouawe-Uruti and Pahaua thrust faults (Barnes and de Lépinay, 1997;Barnes et al, 2010).…”

Section: Geological Settingmentioning

confidence: 99%

Elongate fluid flow structures: Stress control on gas migration at Opouawe Bank, New Zealand

Riedel

Crutchley

Koch

et al. 2018

Marine and Petroleum Geology

Self Cite

View full text Add to dashboard Cite

High-resolution 2D and 3D seismic data from Opouawe Bank, an accretionary ridge on the Hikurangi subduction margin off New Zealand, show evidence for exceptional gas migration pathways linked to the stress regime of the ridge. Although the ridge has formed by thrusting and folding in response to a sub-horizontal principal compressive stress (σ 1), it is clear that local stress conditions related to uplift and extension around the apex of folding (i.e. sub-vertical σ 1) are controlling shallow fluid flow. The most conspicuous structural features are parallel and horizontally-elongated extensional fractures that are perpendicular to the ridge axis. At shallower depth near the seafloor, extensional fractures evolve into more concentric structures which ultimately reach the seafloor where they terminate at gas seeps. In addition to the ridgeperpendicular extensional fractures, we also observe both ridge-perpendicular and ridge-parallel normal faults. This indicates that both longitudinal-and ridge-perpendicular extension have occurred in the past. The deepest stratigraphic unit that we image has undergone significant folding and is affected by both sets of normal faults. Shallower stratigraphic units are less deformed and only host the ridge-parallel normal faults, indicating that longitudinal extension was limited to an older phase of ridge evolution. Present-day gas migration has exploited the fabric from longitudinal extension at depth. As the gas ascends to shallower units it 'selfgenerates' its flow pathways through the more concentric structures near the seafloor. This shows that gas migration can evolve from being dependent on inherited tectonic structures at depth, to becoming self-propagating closer to the seafloor.

show abstract

“…Krabbenhoeft et al [2013] proposed that seepage at Opouawe Bank is structurally driven and parts of the upward migrating gas form gas hydrate resulting in a higher gas/gas hydrate saturation below the seeps. So far, the only gas hydrate samples at Opouawe Bank have been retrieved from shallow gravity cores at Takahe seep site [Luo et al, 2016;Bialas, 2011;Schwalenberg et al, 2010a].…”

Section: Study Areamentioning

confidence: 99%

Marine‐controlled source electromagnetic study of methane seeps and gas hydrates at Opouawe Bank, Hikurangi Margin, New Zealand

et al. 2017

Self Cite

View full text Add to dashboard Cite

Marine controlled source electromagnetic (CSEM) data have been collected to investigate methane seep sites and associated gas hydrate deposits at Opouawe Bank on the southern tip of the Hikurangi Margin, New Zealand. The bank is located in about 1000 m water depth within the gas hydrate stability field. The seep sites are characterized by active venting and typical methane seep fauna accompanied with patchy carbonate outcrops at the seafloor. Below the seeps, gas migration pathways reach from below the bottom‐simulating reflector (at around 380 m sediment depth) toward the seafloor, indicating free gas transport into the shallow hydrate stability field. The CSEM data have been acquired with a seafloor‐towed, electric multi‐dipole system measuring the inline component of the electric field. CSEM data from three profiles have been analyzed by using 1‐D and 2‐D inversion techniques. High‐resolution 2‐D and 3‐D multichannel seismic data have been collected in the same area. The electrical resistivity models show several zones of highly anomalous resistivities (>50 Ωm) which correlate with high amplitude reflections located on top of narrow vertical gas conduits, indicating the coexistence of free gas and gas hydrates within the hydrate stability zone. Away from the seeps the CSEM models show normal background resistivities between ~1 and 2 Ωm. Archie's law has been applied to estimate gas/gas hydrate saturations below the seeps. At intermediate depths between 50 and 200 m below seafloor, saturations are between 40 and 80% and gas hydrate may be the dominating pore filling constituent. At shallow depths from 10 m to the seafloor, free gas dominates as seismic data and gas plumes suggest.

show abstract

A quantitative assessment of methane cycling in Hikurangi Margin sediments (New Zealand) using geophysical imaging and biogeochemical modeling

Cited by 22 publications

References 90 publications

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

Elongate fluid flow structures: Stress control on gas migration at Opouawe Bank, New Zealand

Marine‐controlled source electromagnetic study of methane seeps and gas hydrates at Opouawe Bank, Hikurangi Margin, New Zealand

Contact Info

Product

Resources

About